In general, a diesel engine injects fuel such as diesel into a combustion chamber in a state in which air, which is supplied from the outside to the combustion chamber, is compressed at a high temperature and a high pressure, allows a piston to be moved up and down by an explosive force generated in combustion and explosion processes of mixture gas of air and fuel, and thus generates output power through a rotational force of a crankshaft that is connected to a connecting rod of the piston.
In the engine, fuel efficiency greatly varies according to a mixture ratio (for example, an air fuel ratio) of air and fuel that are supplied to the combustion chamber. When the air fuel ratio gets higher, the output power becomes better, but an amount of emission of nitrogen oxide (NOx), which is harmful to a human body and causes acid rain and photochemical smog as well as pollutes the atmosphere, increases. In contrast, when the air fuel ratio gets low, the output power deteriorates and emission of soot decreases.
Because of the above combustion properties of the engine, the recent diesel engine is adopting an after treatment method of an exhaust gas, which converts the nitrogen oxide (NOx), which is accompanied with the exhaust gas, into harmless water (H2O) and nitrogen (N2) by injecting a urea solution to an inlet portion side of an SCR (selective catalytic reduction), and allowing mixture gas of a urea solution and exhaust gas (or discharged gas) to pass through the SCR. In addition, when the mixture gas combusts, the diesel engine generates sulfur oxide or the like, which greatly disables the catalyst function of the SCR, as well as nitrogen oxide (NOx) and soot.
FIG. 1 is a schematic block diagram illustrating an after treatment device of an engine according to the related art.
As illustrated in FIG. 1, the after treatment device of an engine according to the related art is configured in a type including an exhaust pipe 2 of an engine 1, a urea solution injection section 3, a nitrogen oxide treatment section 4, and an OC (oxidation catalyst) 5.
Here, the urea solution injection section 3 is communicated with the exhaust pipe 2 of the engine 1 and serves to inject a urea solution to the exhaust gas in the exhaust pipe. Mixture gas of the exhaust gas and the urea solution is created while the urea solution and the exhaust gas are mixed with each other.
The nitrogen oxide treatment section 4 is disposed to be spaced apart from the urea solution injection section 3 while communicating with the exhaust pipe 2 of the engine 1 and the urea solution injection section 3, and serves to convert nitrogen oxide (NOx) in the mixture gas of the exhaust gas and the urea solution, which flows in through the urea solution injection section 3, into harmless water (H2O) and nitrogen (N2). The nitrogen oxide treatment section 4 includes an SCR 6 which converts the nitrogen oxide into harmless water and oxygen, and an AOC (ammonia oxidation catalyst) 7 which removes ammonia which slips as it is without reacting in the SCR 6.
The OC 5 is disposed to be spaced apart from the nitrogen oxide treatment section 4 while communicating with the nitrogen oxide treatment section 4 through the exhaust pipe 2, and serves to treat hydrocarbon (HC), carbon monoxide (CO) or the like.
As described above, in the engine 1, when the air fuel ratio gets high, the output power becomes better, but the amount of emission of nitrogen oxide (NOx) increases, and in the opposite case, the output power of the engine deteriorates and amounts of discharge of hydrocarbon (HC) and carbon monoxide (CO) increases.
That is, discharge gas of the nitrogen oxide (NOx) and discharge gas of the hydrocarbon (HC) and the carbon monoxide (CO) are in a trade-off relationship in which when a discharge amount of any one side is increased, a discharge amount of the other side is decreased. Nevertheless, the after treatment device of the engine according to the related art guides all of the exhaust gas, which is discharged from the engine to the outside, to the nitrogen oxide treatment section 4 to remove the nitrogen oxide (NOx) in the exhaust gas, as illustrated in FIG. 1, and guides the exhaust gas, which is discharged to the outside via the nitrogen oxide treatment section 4, to the OC 5 to remove the hydrocarbon (HC) and the carbon monoxide (CO) in the exhaust gas.
This uniform exhaust gas treatment path has a problem in that the sulfur oxide accompanied with the exhaust gas continuously weakens a function of a platinum (Pt) catalyst material which is coated on a plurality of guiding channels (not illustrated) of the SCR 6 of the nitrogen oxide treatment section 4. Moreover, when the hydrocarbon (HC) and the carbon monoxide (CO) also typically add a load to the platinum (Pt) catalyst material, there is a problem in that the nitrogen oxide treatment function of the SCR 6 greatly deteriorates, and as a result, efficiency and durability of the SCR 6 may not be secured.
The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.